Tether tensioning instrument

ABSTRACT

Various methods and devices are provided for tensioning a tether. In one embodiment, a tether tensioning device is provided and includes a tensioning mechanism adapted to couple to a tether extending along a path between at least two bone anchors implanted in adjacent vertebrae. The tensioning mechanism can be adapted to apply a tensioning force to the tether along the path of the tether to thereby move the tether along the path. The device further includes an actuation mechanism movably coupled to the tensioning mechanism such that the actuation mechanism is adapted to effect movement of the tensioning mechanism to control the tensioning force applied to the tether.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/669,909 filed on Nov. 6, 2012, which is a continuation of U.S.application Ser. No. 11/842,371 filed on Aug. 21, 2007 (now U.S. Pat.No. 8,323,294), each of which is hereby incorporated by reference in itsentirety.

FIELD

The present application relates to devices and methods for tensioning atether extending between bone anchors implanted in bone.

BACKGROUND

Spinal deformities, which include rotation, angulation, and/or curvatureof the spine, can result from various disorders, including, for example,scoliosis (abnormal curvature in the coronal plane of the spine),kyphosis (backward curvature of the spine), and spondylolisthesis(forward displacement of a lumbar vertebra). Early techniques forcorrecting such deformities utilized external devices that apply forceto the spine in an attempt to reposition the vertebrae. These devices,however, resulted in severe restriction and in some cases immobility ofthe patient. Furthermore, current external braces have limited abilityto correct the deformed spine and typically only prevent progression ofthe deformity. Thus, to avoid this need, several rod-based techniqueswere developed to span across multiple vertebrae and force the vertebraeinto a desired orientation.

In rod-based techniques, one or more rods are attached to the vertebraeat several fixation sites to progressively correct the spinal deformity.The rods are typically pre-curved intraoperatively to a desired adjustedspinal curvature. Wires as well as bone screws can be used to pullindividual vertebra toward the rod. Once the spine has beensubstantially corrected, the procedure typically requires fusion of theinstrumented spinal segments.

While several different rod-based systems have been developed, they tendto be cumbersome, requiring complicated surgical procedures with longoperating times to achieve correction. Further, intraoperativeadjustment of rod-based systems can be difficult and may result in lossof mechanical properties due to multiple bending operations. Therigidity and permanence of rigid rod-based systems can also hinder orprevent growth of the spine and they generally require fusion of manyspine levels, drastically reducing the flexibility of the spine. To helpremedy some of these issues, a tether and anchor system can be used tocorrect curvature of the spine using a number of anchors disposed withinthe spinal bones connected with tethers extending between them. Theelasticity of the tethers prevents some of the problems with therigidity and permanence of the rod-based systems, although the tethersmust be tensioned after implantation to achieve the desired forcebetween the anchor to correct the spinal deformities.

Accordingly, there remains a need for improved methods and devices forcorrecting spinal deformities and, in particular, there remains a needfor methods and devices for tensioning a tether extending betweenanchors implanted in bone.

SUMMARY

Various methods and devices for tensioning a tether are provided. In oneembodiment, a tether tensioning device is provided for tensioning atether extending along a path between at least two bone anchorsimplanted in adjacent vertebrae and includes a tensioning mechanismadapted to couple to a tether seated across at least two bone anchors.The tensioning mechanism can be adapted to apply a tensioning force tothe tether along the path of the tether to move the tether along thepath. The device can also include an actuation mechanism movably coupledto the tensioning mechanism such that the actuation mechanism is adaptedto effect movement of the tensioning mechanism to control the tensioningforce applied to the tether. The tensioning mechanism and the actuationmechanism can be movably coupled to an elongate shaft. In an exemplaryembodiment, the path can be a substantially straight path.

The tether tensioning mechanism can have a variety of configurations,but in one embodiment the tensioning mechanism can include a wheelrotatably coupled to a distal end of the elongate shaft and adapted torotate to apply a tensioning force to a tether. The actuation mechanismcan include a shaft having a pawl adapted to engage a plurality of teethformed on the wheel to rotate the wheel. The device can further includea stationary handle coupled to a proximal end of the elongate shaft, andan actuator coupled to the stationary handle and adapted to pivot towardthe stationary handle to move the shaft to cause the wheel to rotate.The device can also include a grasping member movably coupled to theelongate shaft and adapted to grasp a tether between the grasping memberand the wheel, and optionally a locking mechanism formed on the elongateshaft and adapted to lock the wheel in a fixed position to lock thetether between the grasping member and the wheel.

In another embodiment, the tensioning mechanism can be in the form of alever arm slidably coupled to the elongate shaft and adapted to slide toapply a tensioning force to a tether. The actuation mechanism caninclude a pusher movably coupled to the elongate shaft and adapted toapply a force to the lever arm to cause the lever arm to slide. A camsurface can be formed on the elongate shaft and it can be positioned tocam the lever arm away from the elongate shaft during sliding movementof the lever arm. The device can also include a grasping member forcoupling the lever arm to a tether and it can be adapted to grasp atether to anchor the tether during tensioning. For example, at least onesurface feature can be formed on a distal end of the lever arm and itcan be adapted to engage a tether.

Spinal anchoring and tensioning systems are also provided, and in oneembodiment the system can include first and second bone anchors having areceiver member and a bone-engaging member, and a tether adapted toextend along a path between the receiver members of the first and secondbone anchors. A tether tensioning device can be adapted to be positionedadjacent to the receiver member of at least one of the first and secondbone anchors and to engage the tether such that the tether tensioningdevice is effective to apply a tensioning force to the tether along thepath to move the tether along the path of the tether. The tethertensioning device can have a variety of configurations, including awheel adapted to rotate to move the tether along the path, and a leverarm adapted to slide and pivot to move the tether along the path. Thetether tensioning device can also include a lumen formed therethroughand adapted to receive a driver for applying a locking mechanism to thereceiver member.

Methods for applying tension to a tether are also provided, and in oneembodiment the method can include grasping a tether extending along apath between first and second bone anchors implanted in adjacentvertebrae, and actuating a tensioning mechanism to apply a tensioningforce to the tether along the path of the tether. The path of the tethercan be a substantially straight line extending across the first andsecond bone anchors. The tensioning mechanism can be formed on atensioning device that is positioned adjacent to one of the first andsecond bone anchors. The method can also include inserting a driverthrough a shaft of the tensioning device, and manipulating the driver tolock a locking mechanism to the bone anchor to thereby lock the tetherin a fixed position relative to the bone anchor. In one embodiment,grasping the tether can include grasping the tether between thetensioning mechanism and a grasping member adapted to grip the tetherand anchor the tether in place.

The tensioning mechanism can have a variety of configuration. In oneembodiment, the tensioning mechanism can include a wheel, and the wheelcan be rotated to apply a tensioning force to the tether. For example,the wheel can be rotated by moving a trigger operatively associated withthe wheel. The trigger can be coupled to a shaft and a pawl that rotatesthe wheel when the trigger is moved. In another embodiment, thetensioning mechanism can include a lever arm slidably and pivotallycoupled to a shaft of a tensioning device. Actuating the tensioningmechanism can include sliding and pivoting the lever arm relative to theshaft to push the grasping mechanism along the path of the tether tothereby apply tension to the tether. Applying a tensioning force to thetether can include actuating a pusher movably coupled to the shaft toslide the lever arm relative to the shaft such that the lever armapplies tension to the tether. Grasping the tether can include graspingthe tether with a grasping mechanism positioned adjacent to thetensioning mechanism such that movement of the tensioning mechanism iseffective to move the grasping mechanism to thereby apply tension to thetether.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments disclosed herein will be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a perspective view of one embodiment of a tether tensioningdevice shown engaging a tether extending through a bone anchor;

FIG. 2 is a side view of the tether tensioning device of FIG. 1 showinga tensioning mechanism including a wheel and ratchet adapted to tensiona tether along its path;

FIG. 3 is a side view of the tensioning mechanism of FIG. 2;

FIG. 4 is a perspective view of the tensioning mechanism of FIG. 2;

FIG. 5 is a perspective view of a grasping member engaging a tetherduring tensioning of the tether tensioning device of FIG. 1;

FIG. 6 is a perspective view of another embodiment of a tethertensioning device having a tensioning mechanism including a lever armand pusher adapted to tension a tether along its path;

FIG. 7 is a side view of the tether tensioning device of FIG. 6 coupledto a bone anchor having a tether extending therethrough;

FIG. 8 is a side view of the tether tensioning device of FIG. 6 coupledto a bone anchor; and

FIG. 9 is a side view of the tether tensioning device of FIG. 6 coupledto a bone anchor and showing a grasping member engaging a tether duringtensioning.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. One ormore examples of these embodiments are illustrated in the accompanyingdrawings. Those skilled in the art will understand that the devices andmethods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope is defined solely by the claims. The features illustrated ordescribed in connection with one exemplary embodiment may be combinedwith the features of other embodiments. Such modifications andvariations are intended to be included within the scope.

Various exemplary methods and devices are provided for tensioning atether extending across one or more anchors implanted in bone. In oneembodiment, a tensioning mechanism is provided that is adapted to coupleto a tether extending along a path between one or more bone anchorsimplanted in adjacent vertebrae. The tensioning mechanism can be adaptedto apply a tensioning force to the tether along the path of the tetheras it extends across the bone anchor(s). The path can be, for example, apath extending along and substantially parallel to a patient's spinalcolumn. The path can, however, have slight departures out of a linearline due to natural curvatures in the spinal column. The path can alsobe substantially perpendicular to an axis of the device, such that thetensioning mechanism applies tension in a direction perpendicular to anaxis of the device. The tensioning mechanism can include an actuationmechanism movably coupled thereto and adapted to effect movement of thetensioning mechanism to control the tensioning force applied to thetether.

FIGS. 1-2 illustrate one exemplary embodiment of a tether tensioningdevice 10 that generally includes an elongate shaft 12 extending from ahandle 14. A tensioning mechanism in the form of a rotatable wheel 18and an actuation mechanism in the form of a pawl 24 are coupled to theelongate shaft 12. The rotatable wheel 18 can be adapted to engage atether 16 seated across one or more bone anchors implanted in bone, andthe pawl 24 can be adapted to move relative to the elongate shaft 12 andthe wheel 18 to effect movement of the rotatable wheel 18 to control atensioning force applied to the tether 16 by the rotatable wheel 18.

The elongate shaft 12 can have a variety of configurations, and it canbe flexible or rigid depending on the intended use. In an exemplaryembodiment, the elongate shaft 12 has a length that allows the distalend of the elongate shaft 12 to be positioned adjacent to a tetherextending along a spinal column, while the proximal end remains externalto the body. This length allows the elongate shaft 12 to extend from thetissue surface to the treatment site, e.g., to a bone anchor implantedin a vertebra. A person skilled in the art will appreciate that theelongate shaft 12 can be made from a variety of biocompatible materialsthat have properties sufficient to enable the elongate shaft 12 to beinserted into the body.

As indicated above, the tensioning mechanism can be in the form of awheel 18, shown in more detail in FIGS. 3-4, that is rotatably coupledto a distal end of the elongate shaft 12 and that is adapted to rotateto apply a tensioning force to the tether 16. The wheel 18 can bepositioned at a distal end of the elongate shaft 12 in a variety ofways. In the illustrated embodiment, the wheel 18 is housed in a recessformed in the distal end of the elongate shaft 12. However, in order forthe wheel 18 to engage the tether 16 to apply a tensioning forcethereto, a distal portion of the wheel 18 can extend distally beyond thedistal-most end of the elongate shaft 12. A person skilled in the artwill appreciate that the wheel 18 can be positioned relative to theelongate shaft 12 in any way that allows a portion of the wheel 18 toengage the tether 16. In addition, the wheel 18 can be coupled to theelongate shaft 12 in a variety of ways. For example, a pivot pin canextend through the wheel 18 and mate to the elongate shaft 12 to allowthe wheel 18 to rotate relative to the elongate shaft 12. A personskilled in the art will appreciate, however, that various othertechniques can be used to rotatably couple the wheel 18 and the elongateshaft 12. The wheel 18 can also include features formed thereon forengaging the tether 16. For example, the wheel 18 can include aplurality of teeth 20 configured to engage the tether 16. The teeth 20can have various shapes and sizes, for example the teeth 20 can beangled to facilitate engagement of the tether 16 as the wheel 18 isrotated.

As indicated above, the device 10 can also include an actuationmechanism that is adapted to effect movement of the rotatable wheel 18to control a tensioning force applied to the tether 16. In theillustrated embodiment, the actuation mechanism is in the form of a pawl24 that is movably coupled to a pusher 22. The pusher 22 is locatedalong a portion of the elongate shaft 12. For example, it can be locatedwithin a longitudinal recess formed along the length of the elongateshaft 12 extending from an actuator adapted to move the pusher 22 to adistal end of the elongate shaft 12. A person skilled in the art willappreciate that the pusher 22 can be coupled to the elongate shaft 12 ina variety of ways, including movably coupled to an outside portion ofthe elongate shaft 12, or being housed in a lumen formed through theelongate shaft 12. The pusher 22 can also have a variety ofconfigurations. In an exemplary embodiment, the pusher 22 has a lengththat allows the distal end of the pusher 22 to mate to the pawl 24,while the proximal end of the pusher 22 is coupled to an actuator, aswill be discussed in more detail below. The actuator can be adapted tomove the pusher 22 in a longitudinal direction along the elongate shaft12 between a distal position and a proximal position to cause the pawl24 to effect rotation of the wheel 18. As indicated above, the distalend of the pusher 22 can be mated to the pawl 24. In an exemplaryembodiment, the pusher 22 is pivotally mated to the pawl 24 to allow thepawl 24 to move into and out of engagement with the wheel 18.

The device can also optionally include a biasing element, such as aspring 31, positioned within the shaft 12 and abutting against the pawl24. When the pusher 22 is in the distal position, the spring 31 can biasthe pawl 24 into engagement with a tooth 20 formed on the wheel 18. Asthe pusher 22 is moved into the proximal position using the actuator,the pawl 24 will pull the engaged tooth 20 on the wheel 18 in a proximaldirection, thereby rotating the wheel 18. This rotation of the wheel 18causes a tensioning force to be applied to the tether 16 along its pathto tension the tether 16 relative to at least one bone anchor 33implanted in the spine. When the pusher 22 is returned to the distalposition, the pawl 24 will pivot out of engagement with the teeth 20,thereby compressing the spring 31. This allows the pawl 24 to slide overthe teeth 20 of the wheel 18 and into engagement with an adjacent tooth20. The pusher 22 can then be moved proximally once again to rotate thewheel 18 to apply additional tension to the tether. A person skilled inthe art will appreciate that any components adapted to rotate the wheelto tension the tether can be used in place of the actuation mechanismdescribed above. For example, a cable can be wound around the wheel andpulling on the cable can be effective to rotate the wheel 18 to apply atensioning force to the tether 16.

In order to facilitate engagement of the tether 16 by the wheel 18, thedistal end of the elongate shaft 12 can include a grasping member 32disposed thereon and adapted to grasp the tether 16 between the graspingmember 32 and the wheel 18. The grasping member 32 can have any size andshape to facilitate grasping of the tether 16, but in the embodimentshown in FIGS. 1-5, it is in the form of an elongate foot extending fromthe distal end of the elongate shaft 12 and positioned substantiallytransverse, e.g., perpendicular, to the elongate shaft 12 and a distancefrom the wheel 18 sufficient to allow the tether 16 to slide between thegrasping member 32 and the wheel 18. The grasping member 32 can also bemovable between a first position in which the tether 16 is not engagedbetween the grasping member 32 and the wheel, and a second position inwhich the tether 16 is engaged between the grasping member 32 and thewheel. The grasping member 32 can be coupled to or formed on a moveableshaft (not shown) that is disposed along or within a lumen formed in theelongate shaft 12. A proximal end of the movable shaft can be coupled toa grasping actuator 34 that can be adapted to effect vertical movementof the grasping member 32 to allow the grasping member 32 to grasp thetether 16 with the wheel 18. For example, the grasping actuator 34 canmove the grasping member 32 between a first unlocked position in whichthe grasping member 32 is located a distance distally from the wheel 18to allow the tether 16 to slide between the grasping member 32 and thewheel 18, and a second locked position in which the grasping member 32is moved proximally towards the wheel 18 to allow the grasping member 32to grasp the tether 16 therebetween.

The tensioning mechanism can also include features to prevent the wheelfrom back-spinning as tension is being applied. In one embodiment, thetensioning mechanism can include a locking mechanism 26 disposed on adistal end of the elongate shaft 12. The locking mechanism 26 can besized to extend between two adjacent teeth 20 formed on the wheel 18,and it can be shaped to allow the wheel 18 to spin in one direction toapply a tensioning force to the tether 16, while preventing the wheel 18from spinning in the opposite direction to maintain the tensioning forceapplied to the tether 16. For example, the locking mechanism 26 can be atriangular member having a first side coupled to the elongate shaft 12,a second side having an angle that corresponds to the angle between thetwo adjacent teeth 20, and a third side substantially perpendicular tothe first side that is effective to block rotation of the teeth in onedirection. A person skilled in the art will appreciate that anymechanism can be used in conjunction with the wheel 18 that can preventback-spinning of the wheel during the application of tension to thetether 16.

As previously discussed, the elongate shaft 12 extends from the handle14 which can have any shape and size, but is preferably adapted tofacilitate grasping and manipulation of the device 10. In theillustrated embodiment, as shown in FIGS. 1-2, the handle 14 includes astationary member 28 and a actuator 30 pivotally coupled to thestationary member 28. As discussed above, a distal end of the actuator30 can be coupled to a proximal end of the pusher 22. The actuator 30can be adapted to pivot toward the stationary member 28 to pull thepusher 22 in a proximal direction to cause the wheel 18 to rotate andapply a tensioning force to the tether 16. A person skilled in the artthat any mechanism can be used to move the pusher 22 along the elongateshaft 12. Moreover, a person skilled in the art will appreciate thateither of the stationary member 28 or the actuator 30 can be movable, orboth of the stationary member 28 and the actuator 30 can be movable.

FIGS. 6-10 illustrate another embodiment of a device for applyingtension to a tether extending across anchors implanted in bone. Thedevice 100 is similar in configuration to device 10 described above, andhas an elongate shaft 112 extending from a handle 114 and having atensioning mechanism and an actuation mechanism coupled thereto. In theembodiment shown in FIGS. 6-10, the tensioning mechanism includes alever arm 118 that is slidably coupled to a distal portion of theelongate shaft 112 and that is adapted to slide to apply a tensioningforce to a tether 116 along the path of the tether 116.

The lever arm 118 can have a variety of configurations, but in oneembodiment as shown in FIGS. 6-9, it has a substantiallyhemi-cylindrical shape to allow the lever arm 118 to be received arounda portion of the shaft 112. The lever arm 118 can be coupled to theelongate shaft 112 in a variety of ways. In the illustrated embodiment,the lever arm 118 is pivotally and slidably coupled to a distal portionof the elongate shaft 112 to allow the lever arm 118 to move distallyand outwardly relative to the shaft 112. In particular, the proximal end118 a of the lever arm 118 can include pins (only one pin 118 p isshown) formed on an opposed inner surfaces thereof that extend intocorresponding cam recesses (only one recess 120 is shown) formed inopposed sides of the elongate shaft 112. The cam recesses 120 can be inthe form of shaped slots that receive the pins and guide the pins alongthe cam recesses 120 to guide movement of the lever arm 118. Forexample, the cam recesses 120 can be adapted to guide movement of thelever arm 118 in a distal and outward direction relative to the elongateshaft 112. This allows the distal end 118 b of the lever arm 118 toslide substantially parallel along the path of the tether 116 to tensionthe tether 116 along its path. Various techniques for moving the leverarm 118 in such a way as to apply the tensioning force along the path ofthe tether 116 will be discussed in more detail below.

In order to further facilitate movement of the lever arm 118 outwardlyaway from the elongate shaft 112, the distal end 112 b of the elongateshaft 112 can include a cam surface 113 formed thereon. In particular,as shown in FIGS. 6-9, the distal end 112 b of the elongate shaft 112can include opposed arms extending outward from the longitudinal axis ofthe shaft 112 such that each arm defines the cam surface 113 on the topportion thereof. The cam surface 113 can slope downwardly, and the leverarm 118 can include a corresponding downwardly sloping surface 119formed thereon that abuts against the cam surface 113. As a result, whenthe lever arm 118 is moved distally, the surface 119 on the lever arm118 will abut against the cam surface 113 on the shaft 112. The camsurface 113 will thus force the distal end 118 b of the lever arm 118 tomove outwardly away from the distal end 112 b of the elongate shaft 112,thereby allowing the lever arm 118 to move a tether along its path.

In order to engage a tether to move the tether 116 along its path, thelever arm 118 can also include one or more surface features or otherengagement mechanisms on the distal end 118 b thereof. For example, thedistal end 118 b of the lever arm 118 can include one or moreprotrusions or teeth formed thereon and adapted to pierce a portion ofthe tether 116 to temporarily couple the lever arm 118 to the tether 116to anchor the tether 116 during tensioning. Alternatively or inaddition, the tether 116 could have a surface featured formed thereon,such as a raised button, to form a surface for the lever arm 118 to pushagainst to apply a tensioning force to the tether 116. In anotherembodiment, a grasping member 132, shown in FIG. 8, can be positioned ata location adjacent to a bone anchor through which the tether 116extends and can be used to grasp the tether 116 to anchor it duringtensioning. In particular, FIG. 8 illustrates the grasping member 132engaging the tether 116 adjacent to the lever arm 118. This will allowthe lever arm 118 to push against the grasping member 132, and therebymove the tether 116. A person skilled in the art will appreciate thatany technique or device known in the art can be used to facilitateanchoring of the tether 116 during application of the tensioning force.

In order to apply a tensioning force to the tether 116, the lever arm118 can be actuated using an actuation mechanism. In the illustratedembodiment, the actuation mechanism is in the form of a pusher 122 thatis movably coupled to the elongate shaft 112 to apply a force to thelever arm 118 to cause the lever arm 118 to slide and apply thetensioning force to the tether 116. The pusher 122 can have a variety ofconfiguration, but in an exemplary embodiment the pusher 112 is in theform of an elongate member that extends along or through a portion ofthe elongate shaft 112 and that includes a distal end (not shown) thatis pivotally mated to the proximal end 118 a of the lever arm 118, and aproximal end 122 a that is mated to an actuator 130, which will bediscussed in more detail below. Actuation of the actuator 130 can beeffective to cause the pusher 122 to move longitudinally along the shaft112 to a distal position in which the pusher 122 pushes against thelever arm 118, causing the lever arm 118 to slide distally and outwardto apply a tensioning force to the tether 116.

The pusher 122 can be moved using an actuator 130 coupled to theelongate shaft 112. In the illustrated embodiment, the actuator 130 ispart of a handle assembly 114 formed on the proximal end 112 of theshaft. The handle assembly 114 can have any shape and size, but it ispreferably adapted to facilitate grasping and manipulation of the device100. In the illustrated embodiment, as shown in FIGS. 6-7, the handleassembly 114 includes a stationary portion 128 formed on and extendingproximally from the elongate shaft 112 for a user to hold the handle ofthe device 100, and the actuator 130 which is coupled to the stationaryportion 128 and is adapted to allow a user to control the tensioning ofthe tether 116. In an exemplary embodiment, the actuator 130 ispivotally coupled to the stationary portion 128 and to the proximal en112 a of the pusher 122. Pivotal movement of the actuator 130 toward thestationary portion 128 can be effective to move the pusher 122 in adistal direction to cause the lever arm 118 to move and slide along thetether 116 to apply a tensioning force thereto. A person skilled in theart that any mechanism can be used to move the pusher 122 to applytensioning force to the tether 116.

Various exemplary methods for tensioning a tether are also provided.While the methods are described in connection with devices 10 and 100, aperson skilled in the art will appreciate that any device can be used.In an exemplary embodiment, the device 10, 100 can be inserted throughtissue, or through an access port disposed in tissue, so that the handlecan extend from the tissue or port on the outside, and the distal end ofthe device 10, 100 can be positioned adjacent to a bone anchor. Thedevice 10, 100 can be positioned adjacent to a tether 16, 116 extendingbetween bone anchors to be tensioning. For example, the device 10, 100can be removably mated directly to the bone anchor, or it can bepositioned against a side of the bone anchor, or spaced apart from thebone anchor. The tether 16, 116 can be grasped to anchor the tether inplace during tensioning, such as with the grasping member 32, 132 ofFIG. 2 or FIG. 7. Once the tether 16, 116 is anchored in place, a forcecan be applied to the actuator 30, 130 of device 10, 100 to move ittoward the stationary member 28, 128 and thereby cause a tensioningforce to be applied to the tether 16, 116. For example, the wheel 18 ofdevice 10 will rotate to push or pull the tether 16 away from the anchorto apply the tensioning force thereto. With device 100, the lever arm118 will slide to push the tether 116 away from the anchor to apply thetensioning force thereto. In an exemplary embodiment, the tether 16, 116is tensioned along its path as it extends longitudinally along thespinal column. This applies the tension in such as a way as to push orpull on the tether 16, 116 without substantially bending the tether 16,116. The proper tension can be applied to the tether 16, 116, and afterthe tether 16, 116 has been locked in the bone anchor to retain thetension thereon, the device 10, 100 can be removed and the tether 16,116 can be released from the grasping member 32, 132. In one embodiment,the tether can be locked between adjacent bone anchors by applying alocking mechanism, such as a set screw, to each bone anchor. A personskilled in the art will appreciate that any mechanism can be used tolock the tensioned tether 16, 116 between adjacent bone anchors.

A person skilled in the art will appreciate that the various methods anddevices disclosed herein can be formed from a variety of materials.Moreover, particular components can be implantable and in suchembodiments the components can be formed from various biocompatiblematerials known in the art. Exemplary biocompatible materials include,by way of non-limiting example, composite plastic materials,biocompatible metals and alloys such as stainless steel, titanium,titanium alloys and cobalt-chromium alloys, and any other material thatis biologically compatible and non-toxic to the human body.

One skilled in the art will appreciate further features and advantagesbased on the above-described embodiments. Accordingly, the disclosure isnot to be limited by what has been particularly shown and described,except as indicated by the appended claims. All publications andreferences cited herein are expressly incorporated herein by referencein their entirety.

The invention claimed is:
 1. A tether tensioning system, comprising: ashaft having a proximal end and a distal end, and a lumen extendingalong a longitudinal axis of the shaft; an actuation handle pivotallyconnected to the proximal end of the shaft; a pusher shaft slidablydisposed within the lumen and pivotally connected to the actuationhandle; and a lever arm pivotally and slidably connected to the distalend of the shaft and pivotally connected to the to the pusher shaft,wherein actuation of the handle advances the pusher shaft longitudinallyalong the shaft to a distal position in which the pusher shaft pushesagainst the lever arm to advance the lever arm distally and outwardly toapply a tension to a tether in a direction substantially perpendicularto the longitudinal axis of the shaft.
 2. The tether tensioning systemof claim 1, wherein the lever arm comprises at least one pin slidablydisposed in a slot in the distal portion of the shaft.
 3. The tethertensioning system of claim 2, wherein the shaft includes a firstdistally sloping cam surface disposed distal to the slot, wherein thelever arm includes a corresponding second distally sloping cam surfacethat slidingly abuts the first cam surface of the shaft, and wherein thelever arm is configured to move distally and outwardly to thelongitudinal axis of the shaft along the first cam surface of the shaft.4. The tether tensioning system of claim 2, wherein the slot of theshaft is disposed at an angle relative to the longitudinal axis of theshaft such that the lever arm is configured to move distally andoutwardly to the longitudinal axis of the shaft as the pin slides withinthe slot of the shaft.
 5. The tether tensioning system of claim 1,wherein the lever arm includes surface features configured to engage thetether.
 6. The tether tensioning system of claim 5, wherein the surfacefeatures include at least one of a protrusion and a tooth.
 7. The tethertensioning system of claim 1, further comprising a grasping memberconfigured to grasp the tether.
 8. The tether tensioning system of claim7, wherein the grasping member is configured to anchor the tether, andwherein the lever arm is configured to apply a force to the graspingmember to tension the tether.
 9. The tether tensioning system of claim1, wherein the lever arm is configured to apply tension to the tetherwithout substantially bending the tether.
 10. The tether tensioningsystem of claim 1, further comprising a stationary handle fixed relativeto the shaft.
 11. A tensioning device, comprising: an elongate hollowshaft having a proximal end, a distal end, and a longitudinal axis, thedistal end including a first cam surface extending at an oblique anglerelative to the longitudinal axis such that the first cam surfaceextends distally and outwardly relative to the longitudinal axis; alever arm pivotally and slidably connected to the distal end of theelongate hollow shaft, the lever arm having a substantiallysemi-circular cross section configured to be received around a portionof the elongate shaft, a portion of the lever arm contacting the firstcam surface; and a pusher shaft slidably disposed in the elongate hollowshaft and pivotally coupled to the lever arm, wherein translation of thepusher shaft longitudinally along the shaft pivots the lever arm aboutthe elongate hollow shaft and distally slides the lever arm along thelongitudinal axis of the elongate hollow shaft.
 12. The tensioningdevice of claim 11, wherein the lever arm includes surface featuresconfigured to engage a tether.
 13. The tensioning device of claim 12,wherein the surface features include at least one of a protrusion and atooth.
 14. The tensioning device of claim 11, further comprising agrasping member configured to grasp a tether.
 15. The tensioning deviceof claim 14, wherein the grasping member is configured to anchor thetether, and wherein the lever arm is configured to apply a force to thegrasping member to tension the tether.
 16. The tensioning device ofclaim 11, wherein the lever arm includes at least one pin, and whereinthe lever arm is pivotally and slidably connected to the shaft with theat least one pin slidably disposed in a slot in the distal end of theshaft.
 17. The tensioning device of claim 11, wherein the portion of thelever arm comprises a distally sloping cam surface that contacts thefirst cam surface of the shaft, and wherein the lever arm is configuredto move distally and outwardly to the longitudinal axis of the shaftalong the first cam surface of the shaft.
 18. The tensioning device ofclaim 11, wherein the elongate hollow shaft includes a second camsurface that is parallel to the first cam surface, the lever arm beingconfigured to contact both the first and second cam surfaces.
 19. Thetensioning device of claim 11, wherein the lever arm is configured toapply tension to the tether without substantially bending the tether.20. The tensioning device of claim 11, further comprising an actuatorcoupled to the elongate shaft configured to advance the lever arm in adirection substantially perpendicular to the longitudinal axis of theelongate shaft.